The invention pertains to the general field of electrolytic loudspeakers and more particularly to a compound electrolytic loudspeaker assembly that has at least two frame-enclosed capacitive transducers which can be arranged in various physical configurations and driven by a single transducer driver unit.
Audio engineers have long endeavored to develop loudspeakers that are relatively free from distortion and that have a frequency response which allows all types of music to be closely reproduced. Loudspeakers are categorized as being either magnetic speakers, moving coil speakers, or non-magnetic, electrostatic speakers/transducers. Due to the fact that the instant invention is categorized as electrostatic, this background art will focus on these types of loudspeakers.
Most conventional electrostatic speakers consist of a flexible center membrane or diaphragm having on each side a fixed electrode, which is designed in the shape of a grid of wires. The wires are placed apart, thereby enabling sound waves, which are generated by the movement of the flexible membrane, to be emitted. The wires are held within a dielectric insulation material, and the flexible membrane is coated with a highly-resistive material. The membrane is suspended within an open-latticed frame between the electrode wires so that when operated, relatively small segments of the diaphragm vibrate as a result of the electrostatic fields acting upon the diaphragm.
Electrostatic speakers are considered to be superior in many respects over the moving-coil type of speakers. However, they have received generally poor acceptance as a result of the mechanical complexity of some designs, low acoustic output, the requirement for a comparatively large radiating area, and a dependence upon the application of a relatively high d-c polarizing bias voltage between the flexible diaphragm and the wire grid electrodes. For example, a typical full range push-pull electrostatic speaker requires a bias voltage of 3500 volts d-c and a driving amplifier with a power capacity of from 60 to 100 watts. Additionally, electrostatic speakers are only able to capably reproduce mid-range and higher audible frequencies. As a result of this it is usually necessary to utilize a bass speaker, which can be connected to the loudspeaker assembly or be a separate module, such as a sub-woofer.
To alleviate some of the above problems, transducers utilizing electrets as the diaphragm have been utilized. The electret diaphragm was thought to be permanently polarized or charged, and therefore did not require a separate polarizing d-c voltage. However, these electrets have been found to be unsatisfactory for application as loudspeakers because the audio level has a tendency to decay.
A search of the prior art did not disclose any patents that read directly on the claims of the instant invention however, the following U.S. patents were considered related:
The U.S. Pat. No. 5,392,358 Driver patent discloses an improved electrolytic loudspeaker assembly that is designed to reproduce a broadband of audio signals. The loudspeaker assembly consists of a thin, non-magnetic capacitive transducer and a transducer driver unit. The transducer consists of a compound diaphragm further consisting of a vibratory center section having attached to each of its surfaces a respective front section and a back section. All three sections of the compound diaphragms are held captive by a frame assembly. The transducer is driven and controlled by the transducer driver unit which couples the audio signal to the transducer""s front and back sections and supplies an unregulated, d-c bias voltage to the transducer""s center section. This patent is assigned MZX, INCORPORATED who is the applicant of the instant application.
The U.S. Pat. No. 4,160,882 Driver patent discloses an electrostatic transducer that functions as a loudspeaker. The transducer consists of two parallel diaphragms each consisting of two plastic sheets, having different charge carrying characteristics, that are sandwiched between an electrically conductive layer. The two diaphragms-are separated by a centrally located perforated electrically conductive sheet and a dielectric material sandwiched between the conductive sheet and each diaphragm. The diaphragm""s two electrically conductive layers are connected across the secondary winding of an audio transformer and the centered electrically conductive sheet is connected to the center tap of the transformer. Thus, when the transformer is applied an audio signal the two diaphragms are driven in a push-pull relation to reproduce the audio.
The U.S. Pat. No. 3,942,029 Kawakami et al patent discloses an electrostatic transducer that can be utilized as either a speaker or microphone. The transducer consists of a vibrating plate or electret diaphragm having a monocharge of positive or negative potential on its surface. The electret diaphragm is made of a thin polymer film that is bonded to a support so that uniform tension exists. A pair of electrically conductive electrodes are brought in contact with opposite sides of the polymer films, and an electrostatic shield, such as a mesh, covers the surface of the two electrodes. A d-c voltage is time-applied across the electrodes to allow the electret to heat to its cure temperature of 120 degrees C. The electret is subsequently cooled to produce a quasi permanent state of electric polarization.
The U.S. Pat. No. 3,705,312 Sessler patent discloses a method for preparing a thin-film electret. The method includes placing a thin polymer film between two electrodes together with a dielectric plate. A voltage of about 30 kev is then applied across the resulting sandwich of elements for about one minute at room temperature and at atmospheric pressure. The method produces charge-densities which are greater by a factor of three than those previously reported.
The U.S. Pat. No. 3,345,469 Rod patent discloses a loudspeaker that operates on electrostatic principles. The speaker consists of a centrally located movable diaphragm which is coated on both sides with a thin, flexible electrically conductive layer. On each side of the diaphragm is located at least one hermetically sealed plastic dielectric sheet. When air or other gas is trapped between the sheets and the diaphragm, a buffer zone is created. To each outer-most dielectric sheet is attached an electrode and to the centered conductive diaphragm is likewise attached an electrode. The two buffer electrodes are connected across the secondary winding of a step-up transformer and the diaphragm electrode is connected through a d-c voltage source to a centertap of the transformer. The transformer""s primary winding is connected to the diaphragm driving signal that is derived from the signal input from a conventional low-impedance amplifier.
The compound electrolytic loudspeaker assembly disclosed herein is designed to reproduce a broadband of the audible spectrum. In its most basic design the assembly consists of:
a) A capacitive transducer comprising a compound diaphragm further comprising a front stator from where extends a front stator electrode, a rear stator from where extends a rear stator electrode and a center diaphragm from where extends a diaphragm electrode,
b) a frame assembly designed to suspend the compound diaphragm in a manner which allows the center diaphragm to flex in a forward and rearward direction, and
c) a transducer driver unit which interfaces with the first stator electrode, the rear stator electrode and the diaphragm electrode. When the unit is applied an audio signal, the unit passes the signal to the compound diaphragm where the signal drives the center diaphragm in synchrony with the applied audio signal.
The capacitive transducer is designed to be used singularly or a plurality of capacitive transducers can be electrically and physically interconnected and operated. Various series, parallel, and series-parallel combinations of capacitive transducers can be arranged to provide an optimum listening performance. As an example, four configurations are presented.
In the first configuration at least two capacitive transducers are placed in a side-by-side horizontal configuration. The second configuration is similar to the first with a space located between each pair of capacitive transducers. In the third configuration at least two capacitive transducers are stacked in a vertical configuration with the lower surface of one transducer placed on the upper surface of a second transducer. In the fourth configuration the capacitive transducers are arranged in a horizontal configuration with the inner surface of a first capacitive transducer abutting with the outer surface of a second transducer. In this fourth configuration each pair of transducers share a common stator. In all of the above configurations the electrodes can be electrically connected so that only three electrodes remain which are connected to the-transducer driver unit which is operated by an external audio source such as a receiver-amplifier.
In view of the above disclosure, it is the primary object of the invention to produce a basic capacitive transducer that can be electrically interconnected and physically positioned with other capacitive transducers to provide various placement configurations, and that can be operated by a single transducer driver unit.
In addition to the primary object of the invention it is also an object of the invention to produce a compound electrolytic loudspeaker assembly that:
does not require the high signal and bias voltage normally required to operate conventional electrolytic loudspeakers,
can be located in various areas and positions that are not possible with current magnetic moving-coil loudspeakers,
is reliable and easily maintained,
can be produced by a process that is easily controlled and is time efficient, and
is cost effective from both a consumer""s and manufacturer""s point of view.